Quantum batteries (QBs) are designed to store energy efficiently for the subsequent use by exploiting various quantum resources.
Subject to the second law of thermodynamics, not all energy injected into the battery can be extracted and the useful part is called extractable work.
Up to now, considerable attention has been mostly focused on identifying useful quantum resources that speed up energy charging dynamics or improve the storage of extractable work.
Distinguished from individual QB cells, collective QB cells do display a quantum correlation-induced speedup in the energy charging process [1]}, [2]}, [3]}, [4]}, [5]}.
Recent works focusing on the Tavis-Cummings (TC) battery and the central-spin (CS) battery have illustrated unfavorable effect of the battery-charger entanglement on the storage of extractable work [6]}, [7]}.
Another effort is to isolate the quantum coherent contribution to the extractable work [8]}.
Despite such progress, it remains vital to establish some general connections between entanglement, coherence, and extractable work.
